Q: Fuel smell and poor fuel economy

asked by on February 15, 2017

I've noticed my gas life shortening and I smell fuel coming from under the hood. My car starts ok with a little hesitation. It shuts off kind of rough though. I've noticed a strange sound as it idles.

My car has 180000 miles.
My car has an automatic transmission.

Hello, There are a number of things that can cause the fuel smell and poor fuel mileage as you describe. I would start with checking the mass air flow sensor as this is a common component that can become dirty or faulty that can cause the kind of hesitation, fuel smell and poor fuel mileage you describe. This is a unit that reads the outside air intake as it enters the engine and relays this to the engine’s computer. The computer then makes adjustments to the fuel supply to the motor based upon these inputs. When this is not working properly, this causes an imbalance in the air/fuel load that is injected into the motor.

A clogged catalytic converter can also cause this kind of problem. When this happens, this causes these gases to be backed up into the exhaust system not allowing the engine to breathe properly. When this happens, the engine is forced to work much harder to expel these gases. This often results in the engine bogging down, hesitating, shaking and causing very poor fuel economy.

A clogged or dirty EGR valve may also cause poor fuel mileage. This is a valve that allows unburnt fuel and exhaust gases to be recirculated into the intake manifold in controlled amounts to be burned with the fuel charge in the motor. When the EGR valve is clogged or dirty (this is very common) it may not function properly causing the engine to idle rough, stall at idle speeds, cause the car to get poor fuel mileage, or emit a strong smell of fuel. I would recommend having an expert from YourMechanic come to your location to take a look at your vehicle to determine what may be causing your car to perform poorly.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Alternator Pulley came off!!

Hello there, many faults will cause the alternator pulley to fail on your 2003 Volkswagen Golf. When the pulley assembly fails on the alternator it is most often due to a seized alternator bearings. To remedy this issue properly the...

I cleaned the ECM/PCM and now my car won't stay on

Whenever the ECM is disconnected the idle control settings the ECM has stored in memory will be cleared. The ECM will revert to the factory-new settings and since the engine now has high mileage and the need for adjustments to...

Transmission is skipping 3rd gear

Hello - a "skipping a gear condition" like this is most commonly a failure of the 3-4 gear clutch pack (for the 4L60E transmission). It is also possible that one of the valve passages in the transmission is damaged, preventing...

Related articles

Understanding the GMC Oil Life System and Service Indicator Lights
Car symbols, or dashboard lights, are a car service reminder. The GMC Oil Life System indicates when and what service your car needs.
How to Get GMC Dealership Certified
GMC car dealerships offer automotive technician jobs to mechanics who are certified through one of the many programs they have available.
A Buyer’s Guide to the 2012 GMC Sierra Hybrid
When When you buy a truck – even a half-ton truck like a GMC Sierra 1500 – you expect to make a trade-off between hauling capacity and fuel efficiency, right? Well, the designers and engineers at GMC don’t think that...